Well Control Incident in the North Sea as Interpreted with Advanced Gas Influx Modelling

Abstract

Handling well control incidents during drilling operations safely and efficiently is of crucial importance, due to the potential danger to crew, rig and environment, as well as the economic aspects. In this paper, we study an actual incident from a North Sea drilling operation, using recent advances in gas influx modelling, which allows for improved understanding of the underlying physical processes, hence enabling more accurate well control simulations. Data has been gathered from a drilling operation where a well control incident occurred, and put into a hydraulic drilling model. This model is enhanced with compositional modelling of PVT properties of the gas/fluid system, allowing for better description of the gas absorption capability of the drilling fluid. Furthermore, effects of non-instantaneous gas loading are handled by a novel kinetic model. Multiple simulations with varying model parameters are run in order to understand how different physical processes can explain the behavior observed in the dataset. Simulations of the case have been compared to the operational data, showing how the different modeling parameters of gas influx impact the simulation prediction performance. A key to safe handling of well control incidents is early detection, but relying only on recordings for topside process conditions limits accuracy and reliability as compared to using the topside data in combination with real-time downhole data and/or advanced mathematical interpretation software. The results show how, by using a combination of downhole modelling and observations, it is possible to obtain a more complete picture of the well conditions throughout the operation. The results also give an indication on early signs that may allow for faster reaction and more confident handling of a gas influx. This case-study of a gas influx scenario with sophisticated gas absorption modelling is the first of its kind, providing useful insights relevant for well control handling and illustrating the benefit of digitalization of drilling operations. By implementing the technology for real-time surveillance, safer and more efficient handling of well control incidents is allowed for, thus reducing the risk of dangerous situations on the rig.